The present invention relates to the field of geophysical exploration. More particularly, the invention relates to an improved, portable apparatus for drilling and underreaming boreholes for containing explosives in land based seismic operations.
Conventional drill equipment uses flow controlled actuators or bias springs within a drill string to drill and to underream a borehole. Large diameter drill stems manage hydraulic actuators and springs together with associated bearings, gears, cams and guides. Conventional equipment using actuators and springs is illustrated in U.S. Pat. No. 5,351,758 to Henderson et al. (1994), which described a hydraulically actuated mandrel for operating expandable reaming dogs. U.S. Pat. No. 4,893,675 to Skipper (1990) disclosed a section milling tool using pump pressure and a coil spring to operate cutters. U.S. Pat. No. 4,614,242 to Rives (1986) disclosed a mechanical connection between an outer pipe and cutter arms for expanding the cutter arms outwardly to enlarge a borehole. U.S. Pat. No 4,431,065 to Andrews (1984) disclosed an underreamer having a hydraulic plunger for deploying cutting arms.
Seismic shot holes in land based geophysical operations have different requirements unattainable with conventional drilling equipment. Shallow seismic shot holes are slender (less than four inches in diameter) and typically extend less than twenty meters deep. Light duty water or air systems provide a fluid for clearing drill cuttings from the borehole. The narrow cross-section of such boreholes and the associated drilling equipment limits the effectiveness of conventional drill equipment because conventional equipment restricts air flow through the narrow drill pipe diameter. Additionally, seismic shotholes preferably have enlarged sections suitable for installation of explosive material. By enlarging one or more portions downhole in a borehole, extra explosive power can be positioned below the surface to enhance the energy coupling of such explosive power to the geologic formations.
A significant limitation of seismic borehole drill equipment is the need for portability and deployment by a single person. Seismic surveys cross extreme terrain sometimes inaccessible to trucks and other vehicles, and environmental and economic issues further limit the potential use of conventional drill operations. Seismic boreholes are typically positioned every fifty meters and are carried by hand from one location to the next. The portability of manheld portable drill equipment is limited by the weight and volume of the drill equipment. The time required to setup, drill, break down, and move such equipment determines the overall operating efficiency of the drill system.
Various slide rail systems offer an alternate method for reaming a drill hole. Slide or guide rail systems have a rail embedded within the borehole diameter to steer the cutting equipment through openings in the main drill stem. Representative reaming bits using guide rails or slide rails are illustrated in U.S. Pat. No. 4,604,818 to Hachiro (1986) which disclosed a pile bore underreaming bucket, and in U.S. Pat. No. 4,407,376 to Inoue (1983) which disclosed an under-reaming pile bore excavator using guide rails to cross the drill pipe axis. Rail type systems are undesirable in slender seismic boreholes because the rails increase fluid or air turbulence within the borehole and thereby lessen the flow available to flush debris from the borehole.
A need exists for an improved, portable drilling apparatus suitable for drilling and underreaming slender boreholes for seismic operations. The apparatus should be highly portable for use in locations difficult to access and should efficiently create boreholes having the desired shape.
The invention provides a portable apparatus for engagement with a drill bit and with a drill mechanism for shaping a seismic borehole wall drilled by the drill bit. The apparatus comprises a drill body having an exterior surface and having a lower end connected to the drill bit, wherein the drill body is selectively moveable by the rotating mechanism. A port extends through the drill body exterior surface, and a reaming bit is movably engaged with the drill body and selectively extendible through the port to contact the borehole wall. A switch is operable by movement of the drill body, and a sleeve is activatable by operation of the switch to move within the drill body and to selectively extend the reaming bit through the port. A cover selectively blocks the port. In various embodiments of the invention, the cover can be integrated within the sleeve, the reaming bit can be retractable within the drill body for operation at another position along the borehole wall, and the force exerted by the reaming bit against the borehole wall can be proportional to a force exerted by the drill body against the drill bit.
In another embodiment, the invention provides a portable apparatus for drilling a seismic borehole wall in soil which comprises a movable drill body having an exterior surface and a lower end, a drill bit attached to the drill body lower end for forming a borehole wall in the soil, a port through the drill body exterior surface, a reaming bit movably engaged with the drill body and selectively extendible through the port to contact the borehole wall, a switch operable by movement of the drill body, a sleeve activatable by operation of the switch to move within the drill body and to selectively extend the reaming bit through the port, and a cover for selectively blocking the port.